Effects of different frequencies of loading on healing in partial rupture of the Achilles tendon in a rat model.

Objective: To determine the histological effects of different frequencies of loading in a healing Achilles tendon following partial rupture.

Design: Experimental laboratory study.

Setting: University of Zimbabwe, Department of Physiology, Animal house.

Subjects: Sixty female Sprague-Dawley rats.

Intervention: Partial tenotomies of the right Achilles tendon were performed surgically. From day 1 post operatively, the animals were allocated to treadmill running at different frequencies (once (OD), two (BD), three (TDS) and four (QID) times daily) up to 21 days. Histological sides of the tendons were made at days 7,14 and 21 and interpreted by a blinded pathologist.

Main outcome measures: Collagen fibre orientation, inflammatory cell populations, fibroblast morphology and neoangiogenesis were observed and scored using the Grande Biomechanical Histological Correlation Score.

Results: Mean weight was 209.67g ±30.14. The best and worst arrangements of collagen were in the QID group (73%) and OD group (46.7%) respectively. These differences were not statistically significant (p=0.487). The BD group had the most mature fibroblast nuclei and the QID tendons had the least mature (p=0.577). Inflammatory cell populations were independent of loading frequency (p=0.132).

Conclusion: Changing the frequency of the same type of loading in a healing tendon does not have an effect on the healing process in partially ruptured Achilles tendons during the inflammatory and proliferative phases.